At birth, both the arteries and veins in the lungs must relax so that blood can flow freely to the lungs and they can function normally and get the baby to "pink up". If the lung arteries do not relax, the resistance for blood to flow into the lungs remains high and blood is diverted away from the lungs leading to the baby remaining blue after birth. If the veins in the lungs do not relax, the lungs can get very wet. By understanding why the lung arteries behave abnormally following chronic oxygen deprivation of the fetus, and why the lung veins function a bit better, we hope to find means of prevention and treatment of Pulmonary Hypertension of the Newborn, a condition that can lead to death of the newborn.